Berkeley DB Reference Guide:

Access Methods

Access method operations

Once a database handle has been created using db_create, there
are several standard access method operations. Each of these operations
is performed using a method referred to by the returned handle.
Generally, the database will be opened using DB->open. If the
database is from an old release of Berkeley DB, it may need to be upgraded to
the current release before it is opened using DB->upgrade.

Once a database has been opened, records may be retrieved (DB->get),
stored (DB->put), and deleted (DB->del).